Ischemia is a condition wherein the blood flow is completely obstructed or considerably reduced in localized parts of the body, resulting in anoxia, reduced supply of substrates and accumulation of metabolites. Although the extent of ischemia depends on the acuteness of vascular obstruction, its duration, tissue sensitivity to it, and developmental extent of collateral vessels, dysfunction usually occurs in ischemic organs or tissues, and prolonged ischemia results in atrophy, denaturation, apoptosis, and necrosis of affected tissues.
In ischemic cardiomyopathies, which are diseases that affect the coronary artery and cause myocardial ischemia, the extent of ischemic myocardial cell injury proceeds from reversible cell damage to irreversible cell damage with increasing time of the coronary artery obstruction.
Critical limb ischemia (CLI) represents the most advanced stage of atherosclerotic, lower extremity peripheral vascular disease (PVD) and is associated with high rates of cardiovascular morbidity, mortality, and major amputation. The incidence of CLI is estimated to be 125,000 to 250,000 patients per year in the United States and is expected to grow as the population ages. PVD prevalence increases dramatically with age and affects approximately 20% of Americans age 65 and older. The current standard of care for individuals with CLI includes lower extremity revascularization, either through open peripheral surgical procedures, endovascular techniques, or lower extremity amputation (i.e., if revascularization has failed or is not feasible). The 1-year mortality rate of patients with CLI is 25% and may be as high as 45% in those who have undergone amputation. Despite advanced techniques in vascular and surgical procedures, a considerable proportion of patients with CLI are not suitable for revascularization. Of these patients, only 20 to 30 percent of CLI patients are undergoing treatment, 30% will require major amputation and 23% will die within 3 months.
Gene therapy strategies to open blocked vessels or stimulate angiogenesis are under active investigation. In a trial of 6 patients with CLI who were scheduled to undergo major amputation, patients were assigned to receive NV1FGF, a non-viral gene therapy expressing fibroblast growth factor 1 (FGF1), 3 to 5 days prior to amputation. NV was administered at 8 intramuscular sites with doses of 0.4 to 4 mg. This trial documented FGF1 transgene expression at all doses up to 3 cm from the injection sites, and that disseminated plasmid into blood vessel was rapidly degraded. In the phase II double-blind, placebo-controlled, multicenter trial conducted in the USA (TALISMAN202), 71 patients with CLI were assigned to receive placebo or 1 of 5 treatment regimens of 2 to 16 mg of NV delivered via 8 intramuscular injections in the affected leg. This trial showed that up to 16 mg of intramuscular NV was safe and well tolerated. The primary endpoint of TcPO2 was increased over baseline in both NV1FGF- and placebo-treated patients, but there was improvement in ulcer healing in the NV1FGF-treated patients. Similarly, Nikol et al. demonstrated in a double-blind, randomized, placebo controlled study of 125 patients that NV1FGF significantly reduced (two-fold) the risk of all amputations, major limb amputations, and there was a trend towards decreased risk of death. These clinical trials demonstrate a safety window of naked plasmid DNA therapies similar to those in our proposed clinical study.